1. Field of the Invention
The present invention relates to a noncontacting electrostatic recording apparatus for forming an electrostatic recording image without bringing a recording head and a recording medium into contact with each other.
2. Description of the Related Art
A multistylus printer is conventionally well known as an electrostatic recording apparatus. This multistylus printer has a recording head constituted by arranging a large number of needle-like electrodes (styluses) in a main scanning direction with equal small intervals therebetween and selectively applies a voltage to each needle-like electrode in accordance with a recording signal to directly perform discharging on paper, thereby forming an electrostatic latent image. In this printer, in order to easily and stably hold an electric charge on paper, specialty paper coated with a high electrical resistance agent is used. Specialty paper of this type, however, is difficult to write something on it with a pen or a pencil and has a problem in storage stability because it is denatured depending on environmental conditions such as a humidity. Therefore, this specialty paper is not preferred as office paper.
In addition, when a gap between the distal end of each needle-like electrode and the surface of paper is large, a discharge electric field from the needle-like electrodes is widened on the paper surface to increase the size of formed dots, thereby making it difficult to obtain a high-resolution recording image. Therefore, a gap material is provided on the paper surface and brought into slidable contact with the distal ends of the needle-like electrodes to ensure a small gap. However, this system has a problem in that the distal ends of the needle-like electrodes are abraded or worn down.
Therefore, as an electrostatic recording system capable of using plain paper and ensuring a small gap between an image medium and the distal ends of recording electrodes, there is a system for forming a toner image on a drum-like intermediate recording medium and transferring the toner image on paper. According to this system, since the size of an apparatus tends to be increased due to the use of an intermediate recording medium, a process of simultaneously performing recording and development is often adopted to avoid the increase in apparatus size. In this case, mostly, a large number of recording electrodes ar aligned in the widthwise direction (main scanning direction) of a developing agent convey path, and a developing agent is selectively transferred from the recording electrodes to the surface of an opposite electrode also serving as an intermediate recording medium in accordance with recording information, thereby developing a toner recording image consisting of dots. In this system, the electrode gaps between the recording electrodes and the opposite electrode must be constant throughout the widthwise direction of the developing agent convey path.
The opposite electrode usually forms a drum and is rotated in order to serve also as a recording medium. In this case, when the opposite electrode is rotated, its circumferential surface tends to swing in the axis or circumferential direction. For this reason, the electrode gap can become locally narrow. When the developing agent is supplied to the narrow electrode gap, the density of the developing agent is increased, and the developing agent becomes dense between the electrodes under pressure. As a result, the electrical resistance of the developing agent, which is normally about 1.times.10.sup.11 [.OMEGA.], is decreased to 1.times.10.sup.3 to 1.times.10.sup.6 [.OMEGA.] at the dense portion. A large current flows in this portion to generate heat, and the developing agent is fused onto the electrodes by the heat and the filling pressure, leading to a serious trouble. When the developing agent is fused on the electrodes, the image resolution is decreased, and the image contrast or visibility is degraded.
When the gap between the recording electrodes and the opposite electrode is increased as the result of swing, the electrical field is widened to cause a problem in that a high-resolution recording image cannot be obtained